1. Field of the Invention
One aspect of the present invention relates to an angle measuring device, and a use thereof.
2. Description of the Related Art
Angle measuring devices are frequently used to detect the steering angle in motor vehicles, for example, in order to determine the steering angle in driving-dynamics control (ESP). Furthermore, it is also necessary to detect the steering angle in motor vehicle control systems which perform an active steering intervention.
In this regard, angle measuring devices are known which can measure the absolute angle within a revolution as well as the number of the revolutions.
In addition, it is known that special demands are placed on the availability of the steering angle measurement due to the possibility of active steering interventions being performed by a motor vehicle control system. Thus, a special demand of a motor vehicle control system of this type being placed on the angle measuring device is to know about the steering angle during the time directly after the activation of the motor vehicle although steering movements or indirect steering movements, provoked by external disturbances, can occur also outside the vehicle operation and must be taken into account.
Published application EP 1 238 891 B1 discloses a steering angle sensor which includes a mechanically coupled counting wheel for detecting the number of revolutions in addition to a code disc whose position and, thus, the absolute angle during a revolution is sensed by sensors. The absolute angle is calculated from a combination of the output signals of two magnetic field sensors and the position of the counting wheel. To be able to perform an absolute angle measurement with this sensor directly after start of the motor vehicle, it is necessary to supply the steering angle sensor with voltage also during an inactive vehicle state, with the result that the electric energy supply of the motor vehicle is highly stressed depending on the duration of this state. Furthermore, the mechanics is relatively complicated and susceptible to wear.
Published application DE 103 44 267 A1 describes a method using a semi-relative steering angle sensor. When the ignition of the vehicle is switched off, the steering angle sensor senses steering wheel movements and stores them electronically. When the ignition is activated, in case disturbances could not be registered, data is used to calculate the current steering angle. A shortcoming of this system resides in the fact that both the sensor and the electronic memory must be supplied with energy in the inactive vehicle state, which burdens the vehicle battery. Furthermore, the angle is subsequently calibrated in the event of disturbances and cannot be sensed directly by the steering angle sensor. The calibration is executed by identifying straight travel during driving, with this straight travel being judged based on the temporal variation of the yaw rate.
It is disclosed in publication EP 0 874 751 B1 to employ a mechanical counter in addition to an angle-of-rotation sensor which measures the absolute angle within a revolution by means of a code disc. In this arrangement, the mechanical counter is coupled mechanically to the code disc, counting the revolutions. Thus, the absolute angle of rotation is sensed at any time also beyond a revolution. Disadvantageous in this construction is the rather complicated mechanics of the code disc and the counter, as well as the torque transmission of the mechanical coupling, which is susceptible to wear and does not function noiselessly.
An angle measuring device, which measures an angle absolutely and with a high angular resolution over a range of several revolutions, with the resulting angle of one or more angular variations being sensed by the device also in the condition of the electronics being deactivated is described herein. The objective is to avoid constant energy supply of the sensors or a technically sophisticated independent waking in the case of a movement to be registered so that the angle measuring device is only active when the motor vehicle is active. Another objective is that the device shall exhibit least possible wear, develop least possible noise and shall be cost-effective.